FIG. 10 illustrates an example of a steering apparatus for an automobile. In this kind of steering apparatus, a steering shaft 5 is passed in the axial direction through a cylindrical shaped steering column 6 and supported by the steering column 6 so as to rotate freely; the front-end section of the steering shaft 5 is connected to the rear-end section of an intermediate shaft 8 by way of a universal joint 7; and the front-end section of the intermediate shaft 8 is connected to an input shaft 3 of a steering-gear unit 2 by way of a different universal joint 7. The steering wheel 1 is supported by and fastened to the rear-end section of the steering shaft 5. During operation, rotation of the steering wheel 1 is transmitted to the input shaft 3, and as the input shaft 3 rotates, a pair of left and right tie rods 4 of the steering-gear unit 2 are pushed and pulled, applying a steering angle to the front wheels.
A tilt mechanism for adjusting the up-down position of the steering wheel 1 and/or a telescopic mechanism for adjusting the forward-backward position of the steering wheel 1 according to the physique and driving posture of the operator are assembled in the steering apparatus for an automobile. Moreover, an electric-powered power steering apparatus, having an electric motor 17 as an auxiliary power source, is assembled in the steering apparatus for making it possible to reduce the force required for operating the steering wheel 1. The tilt mechanism is constructed so that the steering column 6 is supported by the vehicle body 10 by way of the housing 9 of the electric-powered power steering apparatus so that the steering column 6 can pivotally displace with respect to the vehicle body 10 centered around a pivot shaft (tilt shaft) 11 that is arranged in the width direction, and the portion near the rear end of the steering column is supported by a support bracket 12 that is supported by the vehicle body 10 so as to be able to displace in the up-down direction. The telescopic mechanism is constructed such that the steering column 6 is formed by combining together an outer column 13 and an inner column 14 in a telescopic shape so as to be able expand or contract freely; the steering shaft 5 is formed by combining together an outer shaft 15 and an inner shaft 16 so as to be able to transmit torque by a spline joint, and so as to be able to expand or contract; and the outer column 13 is supported by the support bracket 12 so as to be able to displace in the forward-backward direction. In this specification, the “width direction” means the width direction (left-right direction) of the vehicle body unless otherwise stated. Moreover, the “up-down direction” and “forward-backward” direction mean the up-down direction and forward-backward direction of the vehicle body unless otherwise stated.
In a steering apparatus for an automobile in which a tilt mechanism and a telescopic mechanism are assembled, except for an electric-powered type, operation of an adjustment lever switches between an unlocked state in which it is possible to adjust the position of the steering wheel 1, and a locked state in which the steering wheel 1 is maintained at the adjusted position. FIG. 11 illustrates an example of a steering wheel position-adjustment device in which switching between an unlocked state and locked stated is performed by expanding or contracting the dimension in the axial direction of a cam device 20 using an adjustment lever 18. In this device, depending on the expansion or contraction of the dimension in the axial direction of the cam device 20, switching is performed so that it is possible or not possible for there to be relative displacement of the displacement bracket 21 that is fastened to the outer column 13a with respect to the support bracket 12a, and so that it is possible or not possible for there to be sliding movement (relative displacement in the axial direction) between the outer column 13a and inner column 14a. The construction of this kind of cam device is disclosed in detail in JP2002087286 (A).
The outer column 13a is constructed such that a slit 22 is formed in the bottom surface, and by having the front-end section of that slit 22 open up to a front-end edge of the outer column 13a or a through hole in the circumferential direction that is formed in a portion of the outer column 13a near the front-end exclusive of the top end section, the inner diameter of the front half section can elastically expand or contract. A pair of held sections 23 of the displacement bracket 21 are provided in portions that are located on both sides of the slit 22 in the width direction.
In the locked state in which the position of the steering wheel 1 is maintained in the adjusted position, the pair of held sections 23 are strongly held by a pair of left and right support-plate sections 24 of the support bracket 12a. Long tilt holes 25 having a partial circular arc shape centered around a pivot shaft 11 (see FIG. 10) are formed in the support-plate sections 24, and long telescopic holes 26 that extend in the axial direction of the outer column 13a are formed in the held sections 23. An adjustment rod 19 is inserted through the long tilt holes 25 and the long telescopic holes 26. An anchor section 28 is provided on one end section (right end section in FIG. 11) of the adjustment rod 19, and that anchor section 28 engages with one of the long tilt holes 25 that is formed in one support-plate section (right side in FIG. 11) of the pair of support-plate sections 24, making only displacement along this one long tilt hole 25 possible, or in other words, rotation of the anchor section 28 is prevented. Between a nut 29 that is screwed onto and fastened on the other end section (left end section in FIG. 11) of the adjustment rod 19 and the outside surface of the other support-plate section (left side in FIG. 11) of the pair of support-plate sections 24, a thrust bearing 30 and the cam device 20 are arranged in that order starting form the side of the nut 29.
The cam device 20 includes a drive-side cam 31 and a driven-side cam 32. The driven-side cam 32 is supported by a portion near the other end of the adjustment rod 19 so as to be able to displace in the axial direction of the adjustment rod 19. An engaging convex section (boss section) 33 that is provided on the inside surface of the driven-side cam 32 engages with the other long tilt hole 25 that is formed in the other support-plate section 24, and as a result, relative rotation of the driven-side cam 32 with respect to the adjustment rod 19 is essentially prevented. The drive-side cam 31 is supported by the other end section of the adjustment rod 19 so that relative rotation with respect to the adjustment rod 19 is possible, and so that displacement of the drive-side cam 31 in the axial direction is prevented.
By tilting the adjustment lever 18 in a specified direction (generally downward) when adjusting the up-down or forward-backward position of the steering wheel 1, the drive-side cam 31 is rotated and driven. As illustrated in FIG. 12A, by rotating and driving the drive-side cam 31, a convex section 34 that is provided on the inside surface (right side surface in FIG. 11, bottom side surface in FIGS. 12A and 12B) of the drive-side cam 31 engages with a concave section 35 that is provided on the outside surface (left side surface in FIG. 11, top side surface in FIGS. 12A and 12B) of the driven-side cam 32, and the dimension in the axial direction of the cam device 20 contracts. As a result, the space between the inside surfaces of the driven-side cam 32 and the anchor section 28 that face each other expands, the surface pressure at the areas of pressure contact between the inside surfaces of the pair of support-plate sections 24 and the outside surfaces of the pair of held sections 23 of the displacement bracket 21 decreases, the inner diameter of the portion of the front-end section of the outer column 13a inside which the rear-end section of the inner column 14a fits elastically expands, and the surface pressure that acts on the area of contact between the inner-circumferential surface of the front section of the outer column 13a and the outer-circumferential surface of the rear section of the inner column 14a decreases. In this unlocked state, it becomes possible to adjust the up-down position and forward-backward position of the steering wheel 1 within the range that the adjustment rod 19 can displace inside the long tilt holes 25 and an elastic sleeve 27 that is mounted inside the long telescopic holes 26.
As illustrated in FIG. 12B, by tilting the adjustment lever 18 in the direction opposite the specified direction (generally, upward) after the steering wheel 1 has been moved to a desired position, the drive-side cam 31 is rotated and driven, and by the tip-end surface of the convex section 34 of the drive-side cam 31 engaging with a stepped section 36 that is provided on the outside surface of the driven-side cam 32, the dimension in the axial direction of the cam device 20 expands. As a result, the space between the inside surfaces of the driven-side cam 32 and the anchor section 28 that face each other contracts, the space between the inside surfaces of the pair of support-plate sections 24 contracts, the surface pressure at the areas of contact between the inside surfaces of the support-plate sections 24 and the outside surfaces of the held sections 23 increases, the inner diameter of the portion on the front section of the outer column 13a inside which the rear section of the inner column 14 fits elastically contracts, and the surface pressure that acts on the area of contact between the inner-circumferential surface of the front section of the outer column 13a and the outer-circumferential surface of the rear section of the inner column 14a increases. In this locked state, the up-down position and the forward-backward position of the steering wheel 1 are maintained at the adjusted positions.
In the case of this kind of steering wheel position adjustment device, in order to be able to smoothly perform adjustment of the up-down position of the steering wheel 1, it is necessary that the engaging convex section 33 be able to displace (raise or lower) smoothly on the inside of the long tilt hole 25 that is provided in the other support-plate section 24. In order for that, it is necessary to make the width in the forward-backward direction of the engaging convex section 33 a little less than the width in the forward-backward direction of the other long tilt hole 25. By making the width in the forward-backward direction of the engaging convex section 33 less than the width in the forward-backward direction of the other long tilt hole 25 in this way, a space exists between both side surfaces in the forward-backward direction of the engaging convex section 33 and the both side surfaces in the forward-backward direction of the other long tilt hole 25, and the engaging convex section 33 is able to rotate a little centered around the adjustment rod 19 in the inside of the other long tilt hole 25 by an amount corresponding to the size of that space.
When the adjustment lever 18 is tilted downward, a force in a direction that attempts to cause the engaging convex section 33 of the driven-side cam 32 to rotate on the inside of the other long tilt hole 25 centered around the adjustment rod 19 is applied to the driven-side cam 32 due to friction between the tip-end surface of the convex section 34 of the drive-side cam 31 and the stepped section 36 of the driven-side cam 32. By further tilting the adjustment lever 18 downward from this state, the convex section 34 moves in a sliding downward movement toward the convex section 35, being guided by an inclined surface 39 that is provided in a continuous section between the stepped section 36 and concave section 35. When this happens, not only does an inertial force act, but the elastic restoring force from the pair of held sections 23 and the adjustment lever's 18 own weight acts on the drive-side cam 31, and pushes the drive-side cam 31 in the direction of rotation. Then, the reaction force that is applied to the driven-side cam 32 from the drive-side cam 31 rotates the driven-side cam 32 with great force in the direction opposite the direction of rotation of the drive-side cam 31 (left direction in FIGS. 12A and 12B). Due to this kind of rotation of the driven-side cam 32, both side surfaces in the forward-backward direction of the engaging convex section 33 and both side surfaces in the forward-backward direction of the long tilt hole 25 collide, and there is a possibility that a harsh metallic sound (collision sound) will occur. Particularly, when the outer column 13a is made by die casting of a light metal alloy such as an aluminum alloy, the elastic restoring force from the pair of held sections 23 becomes large, and the collision sound becomes large.
JP2003112633 discloses construction in which a concave section is provided in a portion of the inside surface of the driven-side cam that surrounds the engaging convex section, and the inside surface of the driven-side cam comes in contact with the outside surface of the support-plate section only in the portion near the outer diameter of the driven-side cam. However, in this construction as well, as the adjustment lever is operated when adjusting the position of the steering wheel, the driven-side cam turns in the opposite direction from the drive-side cam, and there is a possibility that a metallic sound will be generated. British Patent No. 2,411,453 discloses construction in which protruding wall sections that are formed along the edges on both the front and rear sides of the long tilt hole engage with a concave section that is formed on the inside surface of the driven-side cam. However, in this construction, in order to smoothly perform adjustment of the up-down position of the steering wheel, it is necessary to make the width in the forward-backward direction of the concave section larger than the width in the forward-backward direction of the protruding wall sections. Therefore, even in this construction, there is a space between both sides in the forward-backward direction of the concave section and both side in the forward-backward direction of the protruding wall sections, so when the driven-side cam rotates, there is a possibility that a harsh metallic sound will be generated between the driven-side cam and the long tilt hole.